Our overall objective is to elucidate the mechanisms that control formation of adipose tissues and to determine whether and how these processes are altered by treatments for metabolic diseases. Modern life has provided unparalleled access to food supplies, contributing to a worldwide epidemic of obesity and secondary negative health consequences such as diabetes, fatty liver, cardiovascular disease, and even cancer. Thus there is an urgent need to better understand the mechanisms and molecules that control formation of adipocytes and the expansion of adipose tissue. Adipose tissue is highly dynamic, expanding and shrinking in response to various homeostatic, pharmacologic and dietary stimuli. That new adipocytes form throughout life indicates the presence of a putative adipogenic stem cell. We recently identified such an adipose stem cell by designing, engineering, and studying mice that express molecular reporters in the adipose lineage. These tools enable us to visualize adipose stem cells in vivo, as well as to follow their descendents as they divide, migrate and develop into mature adipocytes. The central focus of this proposal is to use these tools to delineate the in vivo functions and molecular characteristics of our newly discovered adult adipose stem cells. We will define the mechanistic underpinnings of the adipose stem cells and we will understand how physiological and pharmacological stimuli regulate the stem population and the growth of adipose tissue. These studies are designed to elucidate new aspects of adipose biology and metabolic control, highlighting those that are particularly relevant to new therapies for obesity and diabetes.